In the conventional art, an artificial cardiac pump comprises a rotatable impeller so as to be taken and force-fed blood. In general, artificial cardiac pumps can be divided into a group of axial-flow propeller pumps and a group of rotary/centrifugal pumps. Upon comparing the group of the axial-flow propeller pumps with the group of rotary/centrifugal pumps, the group of the axial-flow propeller pumps has an advantage in view of down-sizing. Hereinafter, an artificial cardiac pump with an axial-flow propeller pump will be described.
For example, a conventional artificial cardiac pump comprises a rotor such as an impeller, wherein both ends of the rotor are rotatably supported in a housing and a polar anisotropic permanent magnet is installed in the rotor, and a motor stator such as a rotary magnetic flux generator, wherein the motor stator surrounds with a peripheral of the rotor and is installed in the housing. By magnetic co-relation between the polar anisotropic permanent magnet and the motor stator, the rotor can be rotated with respect to the housing. Under such a structure, a characteristic of an artificial cardiac pump having a typically axial flow propeller pump can be obtained. That is, blood is taken from the front side and force-fed to the rear side by rotating the impeller.
In the above conventional art, a rotor comprises a rotational axial member of which both sides are supported, and impeller wing-components protruded from an outer peripheral surface of the rotational axial member [i.e. Japanese Patent Publication 2001-523983 (pages 23-26, FIGS. 4 and 9)]. Another rotor further comprises a shroud adjoined at an outer peripheral surface of the impeller and coaxially located with respect to the rotational axial member [i.e. U.S. Pat. No. 6,053,705]. In the former case, a polar anisotropic permanent magnet is installed in the rotational axial member. In the latter case, a polar anisotropic permanent magnet is installed in the shroud. In the former case of the artificial cardiac pump, the shroud is unnecessary and a structure thereof can be simplified. Therefore, it is advantageous in view of down-sizing. On the other hand, in the latter case of the artificial cardiac pump, the anisotropic permanent magnet and the motor stator can be alternatively and closely arranged. Therefore, it is advantageous in view of a motor driving effort for rotating a rotor.
However, in the above described conventional artificial cardiac pumps, both sides of the rotor are supported by fixed receiving parts of the housing in a contact relation. Thus, both sides are worn down and burned, such that mechanical loss and damages occur. In addition, blood is apt to be adhered/condensed around abraded powder as a core. Finally, a blood flowing route such as a blood vessel becomes narrower and a thrombus would occur.
Concerning such problems, the inventors provide an artificial cardiac pump having a housing in which a rotor is rotatably supported in a non-contact relation. An improved artificial cardiac pump provided by the inventors will be described with reference to FIG. 3.
As shown in FIG. 3, the improved artificial cardiac pump comprises a cylindrical housing 101, a rotor 103 rotatively supported in the housing 101 in a non-contact relation, a plurality of board-shaped diffuser components 106 protruded from an inner wall of the housing 101 at a rear side with respect to the rotor 103, a rear side fixing body 107 connected with an inner side edge of the diffuser 106 and an axial body 102 fixed on a front end surface 107a of the rear side fixing body 107. Thereby, a fixed axial body 102 is coaxially arranged with respect to a central axis X′ in the housing 101.
The axial body 102 has an outer peripheral surface 102a on which an inner peripheral surface 108a of a sleeve 108 is circularly fitted. The sleeve 108 is rotatably and movably supported with respect to the axial body 102 along an axial direction. A plurality of impeller wing-components 109 are protruded from and fitted on an outer peripheral surface of the sleeve 108. Further, at an outer edge of the impeller, a cylindrical shroud 120 is coaxially fitted with respect to the sleeve 108. The housing 101 includes a circular shroud receiving groove 101a into which the shroud 120 is installed. An inner wall of the circular shroud receiving groove 101 closely confronts with an outer peripheral surface of the shroud 120. The rotor 103 is formed by the sleeve 108, the impeller 109 and the shroud 120.
Inside of the shroud 120, polar anisotropic permanent magnets 110 are radially arranged with respect to the central axis X′. At a front side thereof, a ring-shaped shroud 120 is installed in the shroud 120. The polar anisotropic permanent magnets produce magnet flux perpendicular to the outer peripheral surface of the shroud 120. The permanent magnet 110 produces magnetic flux parallel to the outer peripheral surface of the shroud 120. On the other hand, in the housing 101a motor stator 111 is arranged at a peripheral portion of a shroud receiving grooved portion 101a in order to surround the shroud 120, wherein the motor stator 111 comprises an electromagnetic coil for producing magnetic flux towards the outer peripheral surface of the shroud 120. In front of the shroud receiving groove portion 101 in the housing, a ring-shaped permanent magnet 122 is installed so as to produce magnetic flux perpendicular to the front end surface of the shroud 120.
In accordance with such an improved artificial cardiac pump, rotational force is transmitted to the polar anisotropic permanent magnets 110 of the motor stator 111 by conducting electric current having different phases such as three phase electric current in an electromagnetic coil. Thus, the sleeve 108, the impeller 109 and the shroud 120 of the rotor are integrally rotated around the fixed axial body 102 in the housing 101. Thereby, blood is sucked from the front side and taken into the housing 101. The blood is pressurized by the impeller 109 and flown into the diffuser 106. A hydrodynamic status is recovered to a static status, while the blood is discharged to a rear side. In FIG. 3, a blood flowing route is shown as white arrows.
A blood pressure level at a rear side (downstream) with respect to the impeller 109 is higher than that at a front side thereof (upstream). Under the above structural condition, a load is applied on the rotor itself along a direction from the rear side to the front side. As the result, the front end surface of the shroud 120 is moved towards a front end surface of the shroud receiving groove portion 101a in the housing. However, a repulsion force between the permanent magnets 121 and the permanent magnet 122 is produced since the same magnetic poles face each other. Thus, a contact/collision between the shroud 120 and the housing 101 can be prevented. A portion of the high pressurized blood in the rear side portion of the impellers 109 is flown to an end surface of the shroud receiving groove portion 101a of the housing 101, a rear side surface of the shroud 120, an outer peripheral surface of the shroud 120 and a gap between the front end surface and the housing 101 in order by utilizing a blood pressure difference. Thus, the blood stream is joined with blood at the front side portion of the impellers 109, that is, the blood taken into the housing 101.
The blood pressure difference as described above is utilized to support the rotor 103. That is, the sleeve 108 is supported with respect to the axial body 102 in a non-contact relation. The portion of the high pressurized blood at the rear side portion of the impeller 109 is introduced to a micro gap between an outer peripheral surface 102a of the axial body 102 and an inner peripheral surface 108a of the sleeve 108 from a back side with respect to the sleeve 108 through a gap between the front end surface 107a of the rear fixed body 107 and the rear end surface 108c of the sleeve 108. Then, the blood is joined with the blood taken into the housing by forwardly force-feeding the blood through the micro gap. Accordingly, while the rotor 103 is rotating, blood is flown into the gap between the axial body 102 and the sleeve 108 as a lubricant fluid. The rotating rotor 103 is supported with respect to the axial body 102 in the non-contact relation.
As described above, in the above improved artificial cardiac pump, the rotor 102 is supported and rotated in the housing 101 in the non-contact relation so that mechanical loss (damage) and thrombus which occur in the conventional artificial cardiac pump in which a rotor is supported in a contact relation can be remarkably avoided.
However, the improved artificial cardiac pump as described above comprises a shroud 120 as one of components. Therefore, there are the following drawbacks. The shroud 120 is an outer-most wall of the rotor with respect to a radial direction. At first, unless a weight balance condition is even in the shroud 120, a dynamic balance of the rotor becomes very large in a rotational condition. The rotor cannot be rotated smoothly and such a situation is baneful for the non-contact relation and the rotor would be vibrated. The shroud 120 is the outer-most wall of the rotor with respect to the radial direction. Mechanical loss and damage caused by rotating the rotor in blood cannot be ignored. Particularly, the polar anisotropic permanent magnets 110 that rotate the rotor 103 by confronting with the motor stator 111 is installed in the rotor. Therefore, an unbalanced weight condition is apt to occur in the rotor, even if a degree of the unbalanced weight condition is small.
Second, while the rotor 103 is rotated, blood is (reversely) flown into a gap between the shroud receiving groove portion 101a and the shroud 120 in the housing so that an efficiency of the pump is restricted. If the gap between the shroud receiving grooved portion 101a and the shroud 120 becomes narrower so as to improve the efficiency of the pump, a large shearing force is applied to blood flown therein, because a peripheral rotational speed of the shroud 120 is higher than that of the shroud receiving grooved portion 101a. The large shearing force depends on a rotational speed difference between the shroud 120 and the shroud receiving grooved portion 101a. Under this situation, an outer peripheral membrane of a number of red blood corpuscles are damaged, so that a specific effect of the red blood corpuscle itself is lost and blood is dissolved.
A purpose of the present invention is to resolve the above described drawbacks. An artificial cardiac pump according to the present invention can reduce the above mechanical loss based on a structure that an impeller is supported and rotated in a housing in a non-contact relation and improve pump efficiency.